Rocket grain and method of constructing same



W. A. WEBB May 18, 1965 3 Sheets-Sheet 1 Original Filed April '7, 1959INVENTOR.

WELLS A. WEBB ATTORNEYS May 18, 1965 w. A. WEBB 3,183,665

, ROCKET GRAIN AND METHOD OF CONSTRUCTING SAME Original Filed April 7,1959 3 Sheets-Sheet 2 Q I I IN VEN TOR.

WELLS A. WEBB ATTORNEYS May 18, 1965 w. A. WEBB 3,183,665

ROCKET GRAIN AND METHOD OF CONSTRUGTING SAME Original Filed April 7.1959 3 Sheets-Sheet 3 roe I07 H III INVENTOR.

WELLS A. WEBB United States Patent 3,183,665 RUCKET GRAIN AND METHGD 0F(IQNSTRUCTING SAME Wells A. Wehh, Berkeley, Calif., assignor to HexcelProducts lncx, Berkeley, Calif., a corporation of California Originalapplication Apr. 7, 1959, Ser. No. 894,847, now Patent No. 3,130,672,dated Apr. 28, 1%4. Divided and this application Nov. 19, 1962, Ser. No.260,038 22 Claims. (til. 60-356) This application is a division ofcopending application Serial No. 804,847, filed April 7, 1959, now US.Patent No. 3,130,672.

This invention relates to the structure of expendable rocket grains andthe method of manufacturing the same.

This invention is an improvement of the Structural Rocket Grain andMethod of Rocket Engine Construction described in my copending UnitedStates patent application Serial No. 728,432, filed April 14, 1958, nowabandoned. As described in the aforesaid patent application a cellularmaterial such as honeycomb may be employed in the interior of a rocketto encase oxidant and fuel and to provide in the rocket a structuralsupport which is burned with the fuel. Thus as the fuel is expendedthere is combustion of the supporting members of the rocket. By means ofusing the burnable honeycomb or cellular area support for the fuel andoxidant the maximum structural strength is available during the initialburning phase while still allowing the rocket to lighten its structuralweight load by the burning of the structural members during burn-out.

The principal object of this invention is to provide an improvement ofthe cellular grain by a novel arrangement of separated fuel and oxidantcarrying cellular or honeycomb sandwiches to provide a mechanicalseparation between the oxidant and the fuel which breaks down only underextreme temperatures to allow for the mixture and subsequent burning ofthe burning agent.

A feature and advantage of this invention is that the fuel is normallyseparated from the oxidant so that the danger of accidental combustionis substantially reduced. The device, however, may be readily ignited byraising the temperature of the structure to a high enough range to causea mechanical breakdown of the structure to allow the two ingredients tomix and burn.

Another principal object of this invention is to provide a grainstructure with means to create initial burning on an axial longitudinalcenter line and having means to cause the burning of the grain to be ina conical configuration with the apex of the burning area being on thecenter line and the peripheral edges of the area being rearwardly on theedge of the grain structure.

Another feature and advantage of this invention is that the burning inan inverted conical configuration allows for a more eflicient burningdischarge at a controlled rate so that there is an even, controlledacceleration of the rocket throughout its entire burning cycle ratherthan having an uneven burning for the beginning or other stage ofburning as occurs in many grain structures.

Another object of this invention is to provide means for adjustablycontrolling the burning of the grain from the center outwardly by theprovision of heat transfer rings which causes heat to be conducted atdiiferent rates to difierent areas of the unburned fuel and oxidant.

A further object of this invention is to provide a device to control therate of grain burning employing a moving plug which is timed tolongitudinally forwardly move with respect to the grain structure toregulate the burning of the grain.

A feature and advantage of the movable plug is that the plug functionsas a burning inhibitor so that the burning of the grain does not occurbeyond the plug thereby allowing the burning to be regulated inaccordance with the rate of withdrawal or movement of the plug.

A still further object of this invention is to provide a novel grainstructure employing sandwiches formed of cellular or honeycomb materialencasing an oxidant and/or fuel within the sandwich structure.

A feature and advantage of the sandwich cellular structure is that thesandwiches may contain either a solid or a liquid propellant fuel oroxidant.

Another feature and advantage of the sandwich structure is that thesandwiches may be placed in alternate layers within the rocket structureso that one sandwich layer contains a fuel while the other sandwichlayer contains an oxidant thus mechanically separating the fuel from theoxidant until the temperature for the sandwiches is great enough tomechanically break down the sandwich structure.

A still further feature and advantage of the sandwich structure of thisinvention is that various types of fuels may be employed alternately orin repetitive layers within the rocket grain structure in such a manneras to regulate the thrust of the rocket for different burning phases inaccordance with the fuel properties within the sandwich structure duringthe particular burning phase.

Still a further object of this invention is to provide a novel means offilling honeycomb or cellular sandwiches with a liquid propellantemploying the steps of covering the cellular or honeycomb structure witha skin in which one face of the skin is provided with small apertures,each aperture being coincident with a cellular area. Thereafter thesandwich structure is inserted within a tank where A further feature andadvantage of this invention is that the sandwich structures carrying theoxidant and the sandwich structures carrying the fuel may be stored atseparate places prior to their installation within a rocket to form agrain thus substantially reducing the storage hazards of the burningmaterials.

A still further object of this invention is to provide a novel mechanismand method of assembling a rocket with sandwich structures by theprovision of filling the rocket casing with a liquid adhesive and theninserting layers of sandwich structures within the casing so that eachsandwich structure is submerged within a liquid glue or adhesive at thetime of installation within the casing.

Still a further object of this invention is to provide a novel rocketgrain structure having cellular areas filled with oxidants and fuelsmechanically separated from one another in which the oxidant, fuel andthe separating agents and the areas between same are all formedofsubstantially non-compressive materials so that the thrust generatedfrom the burning of the fuel does not react to cause a collapse or breakdown of the grain structure.

Other objects of the present invention will become apparent upon readingthe following specification and referring to the accompanying drawingsin which similar characters of reference represent corresponding partsin each of the several views.

In the drawings:

FIG. 1 is a sectional view of a rocket employing the or conducting ringsto regulate the burning of the grain.

FIG. 2 is a fragmentary enlarged view of FIG. 1.

g FIG..3 is a cross-section of FIG. 2 taken at line-33.

FIG. 4 is a greatly enlarged view of a honeycomb or cellular structureadapted for use with a liquid propellant or oxidant.

FIG. 5 is a greatly enlarged view of a sandwich structure adapted foruse with a solid oxidant or fuel.

FIG. 6 is a modification of the rocket grain structure shown in FIG. 1employing a movable plug to control the burning of the grain.

FIG. 7 is an enlarged fragmentary view of the embodiment of FIG. 6.

FIG- 8 is a still further enlarged view of the plug mechanism used inthe embodiments of FIGS. 6 and 7.

. FIG. 9 is aschematic view showing the novel process for forming andfilling the grain sandwhich structure and for assembling the sandwichstructures within a rocket casing to construct a rocket grain.

7 FIG. 10 is a longitudinal sectional view showing a furthermodification of a rocket grain structure.

FIG. 11 is an enlarged fragmentary sectional view taken substantially online 2--2 of FIG. 10.

4 FIG. 12 is a fragmentary side elevational view of the winch mechanismshown in a second condition of operation.

Referring now. to the drawings and with particular reference to FIGS. 1,2 and 3 there is provided a rocket A having a case or casing on thefront portion of which is mounted a head or warhead 22 which may be usedfor carrying guidance equipment or explosives. v

.To the rear of the warhead and interior of the casing is the grain 25.The body of the casing is provided on the rear end with an exhaustthroat 28 of reduced diameter through which the exhaust gases from theburning grain are emitted.

. Throat 28.is normally covered by a squib 30 which carries apyrotechnic charge which may be electrically ignited in such a manner asto kindle or fuse the burning of grain 25. 7

Grain 25 isformed of stacked layers of oxidant carrying sandwiches 31and fuel or propellant carrying sandwiches 32.. An ignition tube 35extends axially rearwardly from head 22 through sandwiches 31 and 32opening at the rear facing squib 30.

Sandwiches 31 or 32 may contain a liquid propellant in a structure suchas indicated in FIG. 4 or a' solid propellant as indicated in FIG. 5.The cellular structure forming the sandwich may be honeycomb which maybe in a hexagonal form or in other configurations such as squareor evenrandomly shaped cellular areas.

The endsof the honeycomb core are covered by a first face or skin 40 andthe opposite face, in the embodiment of FIG. 5 which carries the solidpropellant or oxidant, is covered by a similar skin 41. The end walls ofthe honeycomb are shown at 44.

v The sandwich type as shown in FIG. 4, which is adapted particularlyfor liquid propellant or oxidant, is also provided with a first skin 40and on the opposite face there is a skin carrying small apertures 46through which the liquid filler material may be injected into the cells.At least one of the apertures is aligned with each cellular area forthis purpose. Over the skin 45 is a covering skin 48 which completelyseals the apertures to encase the liquid filler within the cellular areaof the sandwichQ It'is important that the solid material such asshow'n'in FIG. 5 or the liquid material shown in FIG. 4 is 'sutficientlyexhausted'of all air or gas particles so that the entire "cellular areais substantially non-compressive. The manner of filling the cellulararea with filler will hereinafter be more specifically described.

The material forming the sandwich should be of a maof the burningof thefuel. This means that the gage of 7 tion and burning of the fuel.

the material, if metal, must be small enough to allow metal to raise tothe burning temperature along with the burning fuel. Cores for thesandwiches 31 and 32 are cylindrical slices as indicated inFIG. 3. Eachof the sandwiches is formed with an interior hole formed to receive awall insert 50 whichforms ignition tube 35. The

edges of the core' are sealed by an inner ring'37 and an outerring 38.

The grain is constructed by stacking alternately oxidant sandwiches 31on fuel sandwiches 32 within the casing 20 of rocket A. The stackedsandwiches are aligned so the holes 49 are in axial alignment'to receiveinsert 50. A sealer 53 seals the outer rim of each sandwich againstcasing 20.

In operation ignition tube 35 is filled with a pyrotechnic material sothat when squib 30 is ignited the temperature within the grain oppositethe squib and ignition tube 35 is' elevated sutficiently t0 fire thepyrotechnic. The heat of the tube causes a break-down of the physicalstructure of the sandwich structure opposite the tube thus releasing andturning into gas the oxidant and fuel under conditions of sulncienttemperature to cause the igni- The conditioned burning of the fuel isdirected from they ignition tube outwardly towards the rim of the casingof the rocket.

The alternation of the layers of oxidant and fuel keep the twoingredients separated until the structural portion of the sandwichissufiiciently broken down by the ele vated temperature to cause therelease of the two substances in gas form ready for burning.

It is highly desirable to control the burning of therocket so that theburning occurs at a controlled ratefrom the center outwardly in a formsimilar to that illus-- trated in FIG. 1 of the drawings. Progressivestages of outward radial burning of the grain are indicated in metallicsubstance highly conductive to heat such as cop per or aluminum.

The area indicated at'60 which is not occupied by rings 57, 58 and 59 isfilled by a low heat conductive material such as polyurethane. Inaddition the space between the outer rim 51 of each of the sandwichesand the inner wall of the casing is filled by a low heat conductivesolid resinous adhesive such as polyurethane indicated at 53.

As can be seen in FIG. 1 when squib 30 is ignited the heat first attacksthe cellular area immediately adjacent the ignition tube 35 and causesthe aluminum forming the honeycomb core and the skin for the core toburn thus releasing'the contents of the cellular area for combus tionaAt the same time heat transfer rings 57, 58 and 59 freely conduct andaccelerate radial outward transfer of heat generated by theburninggrain. The maximum rate of heat transfer is from the ignitiontube to the edge of transfer ring 57 to which point heat is conductedthrough all three of the metal conductors 57, 58 and 59. A slower -.heattransfer occurs to the edge of ring 58 during which heat is transferredthrough two metal conductors 58'and 57. A still slower rate of heattransfer occurs between the edge of ring 58 to the outer rim of element5? when heat is transferred through the single metal conductor 59.Minimum heat transfer occurs in the remaining'area at 60 between theedge of ring 59 and the wall of the casing of the rocket where no heataccelerating metal conductors are provided. V

By means of heat transfer rings the, burning is encouraged to traveloutwardly from the ignition tube in progressively decreasing stagestoward the peripheral edge or outer rim of the casing. Sealer 53prevents fluid communication of gas at the peripheral rim of the grainand prevents burning at the rim.

This structure thus creates a four stage burning pattern as shown inFIG. 1 in which heat transfer by the ring allows a more evendistribution and control of the burning within the rocket grain.

in FIGS. 6 and 7 there is provided another embodiment of the inventionincluding a rocket B constructed similar to rocket A, i.e., having acase 213, a nose cone or warhead 22, a throat 28 with a pyrotechniccharged squib 311. Grain 65 is located between the throat and thewarhead 22. Grain 65 is constructed by placing alternate layers ofhoneycomb material, such as shown in FIGS. 4 and/ or 5, in alternatelayers of oxidant and fuel as indicated at 31 and 32.

The control of the burning is arranged to eflect a substantial conicalburning configuration within the rocket by a movable inhibitor or piston68 which is arranged to be slidably pulled down the length of theignition tube 69 by a pulling mechanism 711.

The sandwich structures forming the sandwiches 31 and 32 are immediatelyabutted next to each other and need not employ the heat transfer ringsas shown in rocket A.

Each of the sandwiches 31 and 32 in rocket B may be juxtaposed relativeto one another with a layer of low heat conductive material 67 betweenadjacent skins in a manner as will be hereinafter described in theprocess described in FIG. 9.

Piston 68 is arranged to move down the ignition tube 6? by mechanism 70via a cable '76 which is pulled by a timer in mechanism 70 at aregulated rate. Tube 69 is filled with a liquid fuel '75 such askerosene to provide back pressure to equalize the thrust pressure causedby the burning of the grain within rocket B. Release of the fluidforwardly of piston 63 is occasioned by a small aperture 82 formedlongitudinallywithin the piston to allow gradual release of the burnablefluid within the column or ignition tube 69 as the piston is drawntowards the front of the rocket. The spray of fiuid fuel adds to theconflagration adjacent the rear face of the piston.

In operation of rocket B when squib 319 is fired the rocket grainimmediately adjacent the ignition tube is caused to burn.

Piston 6d prevents the burning of the sandwich structure beyond the topsurface of the piston. This is due to the nature of burning from thecenter of the sandwich outwardly. It is noted that the break down of thecellular structure forming the sandwiches occurs first in the cellularwalls 44 thus creating an inward break down rather than a forward orlongitudinal break down through the skin of the sandwich structure. Theresults of this type of burning control mechanism provides for controlburning at the center section with the remaining free burning being inthe region of the center outwardly towards the peripheral edge of therocket grain structure. This creates a conical burned area and gives asubstantially even and controlled burning thrust to the rocket.

Piston 68 will inhibit propagation of flame through the ignition tubeand thus may be used to control the rate of flame propagation throughthe grain. More specifically, once grain 32 is ignited, burning willoccur progressively from the combustion chamber toward the upper end ornose of the rocket at a given rate regardless of whether the piston 68is withdrawn through the ignition tube or not. As above indicated, thehoneycomb sandwich which encapsulates the fuel oxidant mixture, is,itself consumable under the heat generated in the combustion chamber,and, depending on the temperature generated in the chamber, so alsowould the piston, itself, and the walls lining the ignition tube beconsumable at a definite rate under influence of the heat generatedduring the burning process.

Therefore, although the inclusion in the rocket grain of a pistonarrangement of the type above referred to may not be used to either stopburning of the grain once it is ignited or to control the minimum rateof burning of the grain, the withdrawal of the piston through theignition tube at a controlled faster rate than the minimum flamepropagation through the grain may serve to accelerate the rate of flamepropagation through the grain via the ignition tube, and to this extentprovides a means for controlling the rate of burning through the grain.

The manner of the assembly of the rocket is schematically illustrated inFIG. 9 wherein a block of honeycomb indicated at is first cut intotubular slices and the center area of each slice is removed as indicatedat 1191 so as to provide a slice of honeycomb core material with acenter cutout and a coaxial outer rim.

A solid ring 38 is placed around the outer rim of the sandwich corematerial and a similar inner ring 37 is placed on the interior edgeforming the central cutout 1111. Thereafter a first skin 41) is gluedwith a suitable compatible resin or cement to the bottom of the core.The core with the bottom face attached may then be filled with a solidfuel or oxidant filler by simply pouring the filler into the cellulararea while in a fluid or plastic state and then conditioning thematerial to set up as a solid.

After the filler material within the core has solidified, a top skin 41is attached to the top face of the material by a facing machine asindicated generally .at 1119. The top face is permanently attached tothe core by a suitable cement or glue. The resulting sandwich product isthen stored in a storage area as indicated at 1111 until the sand wichis to be assembled to form a rocket grain.

If a liquid material is to be filled within the cellular core structure,then after the bottom face has been attached to the core, a top face 45is attached to the core over empty cells. The top face 45 is providedwith a plurality of small apertures 46. Each of the apertures 115 isaligned with one of the cells.

The empty honeycomb core sandwich is then placed within a chamber 117.Chamber 117 is then evacuated through pipes 118 so that the pressurewithin tank 117 and within the cellular areas of the sandwich issubstantially below atmospheric pressure. Under these conditions aliquid oxidant or propellant is fed through line 119 to a storage tank121. The sandwiches are removed from tank 117 and are externally driedas under influence of a blower 123 or by wiping, or otherwise. Afterbeing externally dried, the sandwiches are then fed through machine 16?which applies a face skin 48 on top of the face 45' to completely sealall the apertures 46.

It should be appreciated that the above described method constitutesonly one way of filling a honeycomb sandwich with a liquid filler, andthat other methods and techniques for filling the honeycomb cells may beused or developed according to the particular types of filler materialsemployed and other local conditions without placing any limitation onthe scope of invention as claimed herein.

it is preferable that the sandwiches containing the fuel be separatedphysically a considerable distance from the sandwiches containing theoxidant. Both of the sandwiches while separated are safer to handle inthat the elements necessary for rapid chemical activity are notcombined.

To assemble the rocket grains, a rocket casing such as indicated at isfilled with a liquid glue or plastic resin such as polyurethane. Thesandwiches containing the fuel and oxidant are alternately placed withincasing 135 by a pneumatic ram mechanism 141 The ram mechanism comprisesa platform 1 51 which is arranged to reciprocally vertically move intoand out of the casing. The sandwiches are held against platform 141 byair pressure which forms a Vacuum to hold the sandwiches against theplate. There is always suificient liquid adhesive within casing 135 sothat the next added sandvw'ch is completely submerged under adhesive. Bythis means it is insured that all the spaces between the sandwiches andstrength to the rocket as a mechanical unit during handling, firing andflight.

Referring specifically to FIGS. 10 and 11, there is illustrated afurther embodiment of the invention, particularly designed 'for rocketengines of the type that utilize a propellant which may generate veryhigh internal temperatures in the range of 5,000 C. (9,000 F.) andabove.

The embodiment shown in FIG. 10 is similar to the embodiment describedhereinabove with specific reference to FIGS. 6, 7 and 8 in that theburning of the propellant is controlled by a movable piston type unitwhich is slidably mounted within an axially disposed ignition tube.However, when considering temperatures in the range of 5,000 0., thereis no material known to me from which a piston head could be made thatwould not be consumed by heat. Consequently, the embodiment of FIG. 10contemplates the use of the solid flexible cable or piston 101 ofuniform diameter or cross-section throughout its length, and which ismounted slidably within an ignition tube 102 which extends lengthwisethrough the honeycomb sandwich encapsulated propellant 32. The cabletype piston 101 is made from a flexible plastic heat ablative materialwhich, comparatively speaking, has a low rate of heat transfer and aslower burning rate than the rocket propellant. Nitrocellulose suggestsitself as a possibility forrthis application of use. The walls of theignition tube 102 are likewise lined with a similar material, wherebyboth the cable piston 101 and the walls 102a might be expected toconsume or burn away (endwise) at the same rate, assuming no movement orwithdrawal of the piston within the tube. I

The upper end of the cable piston 101 is anchored to a helically groovedwinch drum 103. As schematically illustrated, the drum 103 may berotated at a controlled speed by a suitable motor unit 104 which isnon-rotatably, although longitudinally slidably keyed as at 105, to thedrive shaft 106 formed as an integral extension of Winch 103. Theopposite end of drive shaft 106 is threadedly rotatably supported in abearing 107. Consequently rotation of the winch drum 103 in a directionappropriate to cause the cable piston 101 to wind itself within thehelical grooves 103 will also (by virtue of the threaded connectionbetween shaft 106 and bearing 107) cause the entire Winch to move to theright as shown in FIG. and thereby maintain the point of winding of thecable on the drum maintained in axial alignment with the ignition tube101. In order to maintain a positive gripping engagement between thecable 101 and the winch drum 103, the helical grooves of the drum may beprovided with relatively sharp teeth capable of embedding themselvesinto the body of the cable under influence of one or more pressurerollers 108 mounted adjacent the winch in pressure biasing contactagainst the outer perimeter of the cable being wound thereon. Thepurpose of maintaining a mechanical interlock between the Winch and thecable is to minimize or preclude the possibility of the cable pistonbeing extruded or forced out the ignition tube under influence of thehigh pressures generated within the combustion chamber of the rocketengine.

J In order to minimize or preclude the flame from the combustion chamberpassing between the piston cable 101 and the lining 102a of the ignitiontube, a viscous lubricant-may be packed between the cable and the wallsof the greases 8 ignition tube and thereby solidly fillany space orclearance that otherwise might exist between the cable. and the tube,and which might permit passage of'the flame therebetween. To preventextrusion of, the lubricant through the upper end of the engine, asuitable packing gland 109 is shown schematically in the upper part ofthe rocket casing.

In operation, the piston cable may be slidably with drawn through theignition tube by a suitable speed control mechanism (notshown) whichgoverns the speed of winding of the winch drum. By withdrawing thepiston cable at a, controlled speed (faster than the minimum rate offlame propagation through the encapsulated grain), the rate of burningof the grain as determined by the rate at which the flame propagatesthrough the grain via the ignition tube, can be accelerated at acontrolled rate.

The oxidant and the fuel have been described as being in alternatelayers. However, it is to be understood that the system of thisinvention may be useful in employing several oxidant carrying layerswith each fuel layer or several fuel layers for each oxidant carryinglayer. It is also believed readily apparent that different fuels couldbe combined in mechanically separated forms in the same manner. It isalso believed further apparent that while the principal embodiments havebeen shown in substantially round cross-section that othercross-sections such as hexagonal, square and the like may be employedwithout departing in any way from the scope of the invention.

It is understood that to make the most efficient rocket embodying thepresent invention, the honeycomb and other sheet material from which thesandwich units are made and the filler materialsgare selected from aclass of materials that will burn with the oxidant thereby contributingto the specific impulse of the rocket and eliminating inclusion in thegrain of any dead weight, i.e., materials that do not contribute to thespecific impulse. In general, aluminum, magnesium and other metallicalloys of thin gauge are suitable for this purpose.

Finally, it is believed that a better regulated control of burning canbe obtained when using oxidant and fuel substances of either highviscosity or solid state whereby as each honeycomb cell is rupturedunder influence of heat, the contents thereof will not immediately spillout and subject the next cell to rupturing heat. Stated otherwise, itmay be anticipated that in using granular substances or liquids of lowviscosity, as each cell is ruptured, the contents will spill outsubjecting the cell behind it to rupturing heat before the contents ofthe first cell will have been consumed. Such conditions may lead toexcessively rapid or uncontrolled burning rates. Therefore, I proposethat when using liquid or granular fuels or oxidants where the aboveproblem may be encountered, that a suitable gelling agent, dispersant,or hinder matrix be added to render the substance semi-solid or highlyviscous whereby the fuel or oxidant will burn in place and not spill outimmediately upon rupturing of the cell.

By way of example, a fuel, such as polyurethane, may be used as a matrixbinder for a granular oxidant, such as lithium perchlorate, dispersedand held in solid suspension within said matrix. Liquid fuels, such ashydrazine, ethylene diamine, and/or a fuel mixture of diethylenetriamine and methylamine (20%) may be gelled to gelatin'or semi-solidstates by addition of appropriate quantities of carboxyl vinyl polymer.Liquid oxidizers, such as bromine pentafluoride might be gelled by theaddition of a fluoro carbon polymer, whereas, an oxidizer,

such as hydrogen peroxide might be gelled with a carboxyl J What isclaimed is:

1. In a rocket structure the combination of: a rocket casing; and aplurality of sandwich members stacked one on top of the other in saidcasing; each said sandwich member being formed of a cellular core andskins sealing the cellular areas of the cellular core; the cellular areaof alternate ones of said sandwich members containing propellant fuelfiller and the cellular layers of alternate other ones of said sandwichmembers containing an oxidant filler.

2. In a rocket structure the combination of: a rocket casing; aplurality of sandwich members stacked one on top of the other withinsaid casing; each said sandwich member being formed of a cellular core;a pair of skins covering the broad face of each core to seal thecellular area of each cellular core; the cellular areas of said sandwichmembers containing propellant fuel and oxidant fillers; and an ignitiontube extending through said sandwich members in axial alignment with thelongitudinal axis of said rocket casing; said ignition tubecommunicating with the middle portion of each said sandwich memher.

3. A rocket structure according to claim 2 and wherein said ignitiontube extends at an angle substantially normal to the broad face of theskin of said sandwich members.

4. A rocket structure according to claim 2 and wherein said sandwichmembers are formed of material having a burning temperaturesubstantially below the burning temperature of the fuel filler.

5. A rocket structure according to claim 2 and wherein the outer edge ofeach sandwich member is sealed against the wall of said rocket casing.

6. A rocket structure according to claim 2 and wherein each saidsandwich member is sealed with fluid tight sealing means having low heatconductivity in the areas between the sandwich members and said rocketcasing and between the sandwich members and said ignition tube.

7. In a rocket structure the combination of: a casing; a rocket grainwithin said casing; said rocket grain formed of a plurality of stackedsandwich members; each sandwich member being formed of a cellular corewith substantially flat skins covering the two broad faces of said coresand sealing the cellular areas formed by the cores; first ones of saidsandwich members being completely filled with an oxidant filler; secondones of said sandwich members being filled with a fuel filler; anignition tube axially aligned with the longitudinal axis of said casingand disposed substantially normal to the broad faces of the skin of saidsandwich members; and means to regulate the burning of the grain.

8. A rocket structure according to claim 7 and wherein said burningcontrol means comprises heat transfer rings mounted between adjacentsandwich members; said heat transfer rings being coaxially mountedrelative to said ignition tube and having an outer diametersubstantially less than the sandwich members; said heat transfer ringsbeing formed of a material having a high heat conductivity.

9. A rocket structure according to claim 7 and wherein said burningcontrol means comprises a plurality of rings mounted between adjacentsandwich members; each said ring being formed of a highly heatconductive material; each said ring being coaxially mounted relative tosaid ignition tube and having an inside diameter substantiallycoincident the outer diameter of the ignition tube; first ones of saidheat transfer rings having a first diameter substantially smaller thanthe outer dimension of said sandwich members; second said heat transferrings having an outer diameter greater than the first said heat transferrings and smaller than the outer dimension of said sandwich members; andfiller means between adjacent sandwich members; said filler means havinga heat conductivity substantially lower than said heat transfer rings.

10. A rocket grain structure according to claim 7 and said pistonforwardly through said tube at a controlled t rate; liquid filler meanswithin the forward end of said tube; and fluid filler escape means toform a controlled fluid communication path from said tube past saidpiston.

12. In a rocket grain structure the combination of: stacked sandwichmembers; said sandwich members being filled in alternate layers with anoxidant and a fuel; and burning control means in the center of saidgrain and intersecting all said sandwich members to cause burning ofsaid grain to extend freely along said burning control means at acontrolled rate and thence outwardly from the center portion of saidgrain.

13. A method of assembling a rocket grain casing in which the rocketgrain is formed of individually sealed cellular sandwiches comprisingthe steps of: filling the rocket casing with a liquid adhesive filler;and sequentially inserting the cellular sandwiches in stacked relationinto said casing below the surface of the adhesive filler while theadhesive is in a plastic condition thence conditioning the adhesive toset to a solid state.

14. In a rocket structure, the combination of .a rocket casing definingan interior combustion zone in communication with an exhaust port, arocket grain in said casing comprising individual capsules filled withpropellant; the material from which said capsules are made beingconsumable under influence of heat generated by the burning of saidpropellant; a hollow ignition tube extending from said combustion zonethrough the encapsulated grain; an elongate piston element having auniform cross-section throughout its length snugly slidably mounted insaid ignitron tube; said piston element disposed, prior to burning ofsaid grain throughout the length of said ignition tube and with its freeend adjacent said combustion chamber; and means in said casing forslidably withdrawing said elongate piston element through said ignitiontube to control the maximum rate of flame propagation from saidcombustion zone through said grain via said igition tube.

15. The combination of claim 14 and wherein a viscous lubricant isdisposed between said piston element and the walls of said ignition tubeto act as a lubricant and as a flame barrier to barricade againstpropagation of flame in bthe space defining the clearance between thepiston and tu e.

16. The combination of claim 14 and wherein said piston element is madeof an integral length of comparatively slow heat conductive and heatablative material.

17. The combination of claim 16 and wherein both said piston element andthe walls of said ignition tube are made of the same material.

18. The combination of claim 14 and wherein said piston element is madeof relatively flexible material; and wherein said means for withdrawingsaid cable through said ignition tube comprises a winch mechanism aroundwhich said piston element is adapted to be wound.

19. A solid propellant cartridge comprising: an elongated body ofpropellant presenting an end surface for burning and having a centralbore therethrough; a propellant material core extending through saidbore to present an additional end surface for burning; and means forshifting said core longitudinally relative to said body of propellantduring burning of said cartridge so as to change the relative positionof said end surfaces and thus modify the burning rate.

20. A solid propellant cartridge comprising: an elongated body ofpropellant presenting an end surface for burning and having a centralbore therethrough, shiftable plug means in said bore operable to providea pilot flame material.

22. A rocket structure including: a rocket casing; a a

plurality of sandwich members stacked one on top of the other withinsaid casing; each said sandwich member being formed of a cellular core;a pair of skins covering 12 V A a the broad face of each core to sealthe cellular area of each cellular core, the cellular areas of saidsandwich members containing propellant fuel and oxidant fillers.

' References'fiited by the Examiner UNITED STATES PATENTS 2,408,252 9/46De Ganahl 60- 356 2,759,418 8/56 Ross et al 6035.6

2,802,332 8/57 Orsino 60-35.6 10 2,977,885

4/61 Perry et al. 60- -35.6

SAMUEL LEVINE, Primary Examiner.

7. IN A ROCKET STRUCTURE THE COMBINATION OF: A CASING; A ROCKET GRAINWITH SAID CASING; SAID ROCKET GRAIN FORMED OF A PLURALITY OF STACKEDSANDWICH MEMBERS; EACH SANDWHICH MEMBER BEING FORMED OF A CELLULAR COREWITH SUBSTANTIALLY FLAT SKINS COVERING THE TWO BROAD FACES OF SAID CORESAND SEALING THE CELLULAR AREAS FORMED BY THE CORES; FIRST ONES OF SAIDSANDWICH MEMBERS BEING COMPLETELY FILLED WITH AN OXIDANT FILLER; SECONDONES OF SAID SANDWHICH MEMBERS BEING FILLED WITH A FUEL FILLER; ANIGNITION TUBE AXIALLY ALIGNED WITH THE LONGITUDINAL AXIS OF SAID CASTINGAND DISPOSED SUBSTANTIALLY NORMAL TO THE BROAD FACES OF THE SKIN OF SAIDSANDWICH MEMBERS; AND MEANS TO REGULATE THE BURNING OF THE GRAIN.